It is known to produce disc wheels of steel from two parts by pressing a wheel dish made oversize in respect of the inside diameter of the well base of the rim into the well base of the rim which has been calibrated, ready for fitting, by expanding or upsetting, and by subsequently welding the two parts to one another.
Furthermore, it is known to subject complete disc wheels, after the welding of the rim and wheel dish, to a subsequent trueing operation by bending, expanding or upsetting and, if appropriate, to additional machining, in order to improve the concentric and planar running of the wheel made from cold-worked parts. This is generally carried out in such a way that, by means of plastic working of the wheel contact region of the wheel dish and/or of the two rim shoulder parts (tyre seating faces), with mutual influencing of these two axial and radial reference planes, the geometrical variations are permanently reduced (German Auslegeschrift 1,909,353; German Offenlegungsschrift 2,221,210; German Offenlegungsschrift 2,224,027; German Offenlegungsschrift 2,224,109; and, German Offenlegungsschrift 2,314,858).
It is also known to expand or upset the rims of cast disc wheels for the purpose of producing an exact geometrical shape (German Auslegeschrift 2,442,785).
The energy-saving measures of vehicle manufacturers also include savings of weight on the motor vehicle. The manufacture of disc wheels made of light sheet metal is suitable here, since a weight reduction of approximately 40% in comparison with the conventional steel disc wheels is to be achieved thereby. In particular, however, considerable difficulties arise in the production of such wheels of light sheet metal according to the same processes practiced hitherto in the production of wheels made of sheet steel. Although an oiled or greased light-metal wheel dish can be drawn into the rim without excessive scoring, a strong pore formation occurs, during welding, as a result of the harmful hydrocarbon lubricants. Moreover, in the case of the oversize insertion tolerance, which is necessary for a firm fit, deformations arise, such as buckling and tilting of the wheel-dish tabs, which leads to a defective, non-parallel fit between the wheel-dish tabs and the well base of the rim, the air gap which arises resulting, moreover, in welding defects. In the case of the clean surfaces required for the purpose of welding, it is virtually no longer possible to all to join the parts into one another properly, with oversize, by pressing in. In the pressing-in operation, a severe seizing of the material together with the resulting cavities and scores would occur, which would prevent a parallel fit of the dish in the rim and lead to weld defects which are the starting point for weld cracks and wheel fractures resulting therefrom. On the other hand, the seizing would lead to considerable deviations from concentric and planar running of the wheel.